Field of the Disclosure
Embodiments generally relate to input sensing and, in particular, to a matched filter for a first order sigma delta capacitance measurement system and a method to determine the matched filter.
Description of the Related Art
Input devices including proximity sensor devices (also commonly called touchpads or touch sensor devices) are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by a surface, in which the proximity sensor device determines the presence, location, and/or motion of one or more input objects. Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems (such as opaque touchpads integrated in, or peripheral to, notebook or desktop computers). Proximity sensor devices are also often used in smaller computing systems (such as touch screens integrated in cellular phones).
Proximity sensor devices generally include sensor electrodes for sensing the presence of input objects. A processing system drives the sensor electrodes and receives signals with the sensor electrodes. The processing system also processes the signals received with the sensor electrodes in order to detect the presence of input objects.
A processing will typically include analog processing circuitry that samples and filters signals received from sensor electrodes. This analog circuitry typically includes a charge integrator, a demodulator, filtering circuitry, and the like. One issue with analog circuitry, however, is that it occupies a large amount of physical area within a chip. Thus, it would be beneficial to reduce the amount of analog circuitry used in the processing system.